1. Field of Invention
The invention relates to a magnetic rotation detector used to detect a rotational speed of a wheel of a vehicle, a vehicle control apparatus employing the magnetic rotation detector, and a method of making a determination on an abnormality in a magnetic rotor.
2. Description of Related Art
A magnetic rotation sensor is known as a device for detecting a rotational speed of a wheel in a vehicle (e.g., see Japanese Patent Application Laid-Open No. 3-59416 (pages 3 and 4, FIG. 1)). A magnetic rotation sensor of this kind is composed of magnetic bodies and a detector. The magnetic bodies are disposed at equal intervals on an outer periphery portion of a rotor that rotates in synchronization with an object whose rotational speed is to be detected. The detector is a pick-up such as a hall device or the like, and is disposed outside the rotor while facing it. If the rotor rotates, the magnetic bodies disposed on the outer periphery of the rotor cause a change in magnetic flux around the pick-up. The pick-up detects the change in magnetic flux and outputs a signal. Thus, movements of the magnetic bodies causing the change in magnetic flux, namely, rotation of the rotor can be detected on the basis of the signal output from the pick-up.
A magnetic rotation sensor of this kind is disposed on a rotational axle for wheels or the like. However, since a structure for mounting the magnetic rotation sensor cannot be sealed, foreign matters inevitably penetrate into the sensor. If iron fragments or the like have penetrated thereinto, they may adhere to the magnetic bodies disposed on the outer periphery portion of the rotor and may disturb a change in magnetic flux. If the change in magnetic flux is thus disturbed, a fluctuation in rotational speed is erroneously detected even though the rotor itself rotates at a constant speed.